Devices and methods for assisting valve function, replacing venous valves, and predicting valve treatment successes. In an exemplary embodiment of an endograft body configured for expansion within a luminal organ, the endograft body comprises (a) a first portion having a proximal end defining a proximal end aperture and a distal end defining a distal end aperture, the first portion configured to increase a velocity of fluid flowing therethrough, (b) a second portion having a second portion proximal end defining a second portion proximal end aperture and a second portion distal end defining a second portion distal end aperture, wherein the distal end of the first portion is adjacent to the second portion proximal end, and (c) a valve portion positioned at or near the second portion proximal end, the valve portion configured to receive the fluid flowing through the distal end aperture of the first portion.
